What is Pycnodysostosis?

Pycnodysostosis (PYCD), also spelled pyknodysostosis, is an inherited disease that causes the bones to be abnormally dense while also creating certain bone deformities.

The bones of people with PYCD are brittle and can break easily, even under minimal stress. Fractures are common in affected people's legs, feets, jaws, and collar bone.

People with the disease are abnormally short—less than five feet in height and often much shorter. They are susceptible to a curved spine (scoliosis), and the collarbone is often deformed as well. People with PYCD also have significantly shorter finger bones and their nails are small or absent.

People with pycnodysostosis often have characteristic features including a prominent nose, protruding forehead, and small jaw. Their teeth can be late in coming in, may be missing or irregular, and are prone to cavities. The skull is typically deformed, with the “soft spot” on the top of the head failing to close.

Many scientists believe that 19th-century French painter Henri de Toulouse-Lautrec had PYCD, though the disease was unknown at the time.

How common is Pycnodysostosis?

The frequency of PYCD is unknown, however the disease is very rare.

How is Pycnodysostosis treated?

There is no treatment for the cause of PYCD, however injections of growth hormone have been shown to improve height. Plastic surgery can help correct deformities of the face and jaw.

Dental care will be necessary as people with PYCD are prone to cavities and may be missing teeth. Orthodontia is an option for improving the overall look to the teeth.

People with PYCD need to be careful with their bodies to avoid bone fractures. Exercise should be limited to low-impact activities such as swimming.

What is the prognosis for a person with Pycnodysostosis?

The prognosis for a person with PYCD is generally good. He or she will be prone to fractures, but with care, lifespan can be normal or near-normal.